Python - Application logic - Help with understaing

Hello, i am making an application that has GUI and some classes. I ran into a problem of getting an idea for the logic.
here is a brief description of the program:
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Structure:
3 modules
Module 1 - **dataPreparation.py** -responsible for string processing - made of several classes and methods that receive PATH to directory, collect all files in a LIST, after that for each file based on type of file name it sorts it out to appropriate categories that can be accessed through class instances.

Module 2 - **gui.py** - Responsible for GUI. It crates a simple GUi-layout that offer BROWSE button (to get the PATH), QUIT button to exit application, LISTBOX that lists subfolders from the PATH, and BATCH button that must execute the main processor.

Module 3 - **vntProcessor.py** - Responsible for processing of collected data. This module is based of an API of another application. It receives the values from the BATCH-button and invokes specific methods based on sorting that was performed using MODULE 1.

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So, here is the logic problem that i encountered, and i wanted to ask what is the best way to handle it.